This disclosure relates to image processing apparatuses and methods of processing color image data that successively receive color image data of successive frames, correct the received color image data in accordance with differences of the image between frames, and output corrected color image data.
Liquid crystal display panels have a characteristic that ON-OFF response time of liquid crystal cells is longer than a frame period of moving images. In order to shorten the response time of liquid crystal cells of the display panel, an overdrive technique is widely utilized. That is, color image data of the previous frame is stored in a frame memory and compared with color image data of the current frame, and corrections are made in accordance with changes of the image between the frames.
FIG. 8 is a block diagram that shows a construction of a conventional image processing apparatus that performs overdrive. The image processing apparatus 30 shown in FIG. 8 includes a frame memory 34, OD amount calculation block 36 that calculates amounts of overdrive, and an adder 38.
Color image data of the current frame (RGB input) is stored in the frame memory 34. The OD amount calculation block 36 calculates amounts of overdrive based on R-, G-, and B-element values of respective pixels of a previous frame read from the frame memory 34 and R-, G-, and B-element values of corresponding pixels of the current frame. Corrected color image data (RGB output) is generated by adding, by using the adder 38, R-, G-, and B-element values of respective pixels of the current frame and the calculated overdrive amounts and output.
The frame memory 34 that stores color image data of the previous frame need to have a large memory capacity in order to store R-, G-, and B-element values of respective pixels. In order to reduce a required capacity of the frame memory, Japanese Laid-open Patent JP 6-237396 (Patent document 1) proposes to perform a high-rate compression of input image signal and to store the compressed image information in the frame memory. However, rate of reduction of the memory capacity in the technique proposed by Patent Document 1 is limited by the limitation of compression rate.
On the other hand, US Patent Publication US 2005-008078 (Patent document 2) proposes to supply Y-element values alone from the frame memory and to perform LAO (level-adaptive overdrive) process only to the Y-element values. According to Patent document 2 (3rd embodiment and FIG. 5), a human eye recognizes a significant improvement of display characteristic by performing LAO process only to Y-element (luminance element). Accordingly, amount of task of the LAO process block can be decreased.
The technique proposed by Patent document 2 only requires storing Y-element values in the frame memory. Accordingly, it enables to reduce the capacity of the frame memory by ⅓ compared with a case that all of R-, G-, and B-element values are stored. However, when the overdrive is performed by only using Y-element values as the previous frame color image data, display quality may be degraded due to, for example, color blurring at boundaries between objects with different colors.